Air preheater for furnaces



Nov.- 6, 192a w. H. OWEN AIR PREHEATER FOR FURNACES Filed Aug. 16, 1924 //7 ale/776x. mam/M per Patented Nov. 6, 1928.

* E KSTATES ,PLATENT OFFICE.

Paulina-ran Ion rmmacns.

Application fled August 16, 1924, Serial in. 732,512, and a GreatBritain September a; 1923.

This invention has reference to the application ozfpre-heated air to furnaces. Accordmg to the mventlon the air pre-heater ar rangement comprlses two sections or air heaters, viz a'preli-minary heater and a final 10. nearer to the furnace than the other, and

therefore being hotter forms a final or extraheater for that portion of the air whichpasses through it.

The Wholeof the incoming air is caused to v pass first through the preliminary heater,

that is to sa nace, thus aving its temperature partly raised. Itis then divided into two parts or currents one part goin direct into the furnace below the grate, t at is into the ashpit.

' Theother part is passed through the final and hotter heater, viz :that nearer to the furnace, thus having its temperature raised still higher (that is'tosay, becoming extra-heated) and being then'led to the space above the furnace grate, where it min les with and actively promotes the combustlon'of the fuel e Irrthe accompanying diagrammatic drawi gs. 1 and 2 illustrate in side andfront view, and partly in section on the lines :u-w and yy, respectively, the application of the invention-tom water-tube boiler having an ordinar chain-grate.

a is t e outer casing or'shell of the boiler, and b is the chain or other automatic grate which is arranged in the boiler furnace and is of an convenient type. c is the feed hop- 40- per an (1 represents the front wall of a closed ashpit a'rrangement. e is the ordinary heat-radiating or combustion arch, and f is the boiler up-take. I 2

9, 9 represents the two part air-heater arrangement in which the incoming air for supportingoombustion is pre-heated in the manner above'referred'to, b the'heat of the waste gases on their way to t funnel or u take f;

is the'preliminary hea r, and g t e final eater. V

. Each heater section g,.g* is of the tubular or any other convenient and the part g is placed asclom to the rnace as possible,

so as to receive the waste. gases in their hot-- test state immediately they leave the heating surface the one remote from the fura the air being would be if it had also passed through thev 9 re resents the economizer forQheating the fee water which is placed between them,

and serves to separate the two heater secl tions 9, g".

' In the example shown this economizer comprises a hotglr casing containing a nest of aving inlet and outlet pipes water-tubes such as g g. p The upper or preliminary heater or section 9 receives all the incoming air and raises its temperature, such air entering by a rear opening in the middle'of the heater and flowing to the right and left as indicated by the arrows 1. The lower and hotter or final heater or section 9", viz the one nearer to the furnace, receives at each end a portion of this air from the other section in the known man ner and gives it the extra heat.

This extra-heated air is then led from an opening j at the middle of the extra heater g". (according to the type of boiler or furnace) by any convenient arrangement of passages or ducts h (with regulating valves or dampers) intothe top of the furnace viz above the chain grate I),

In the example shown the ducts it communicate with the ends of a transverse air passage iarranged above the arch 6, suitable vents'i being provided in the latter, so that the extra-hot air from the final heater 9? mingles with the gases and volatile matters given 0135- by the fuel and throws them into intense combustion, but this occurs well away from the grate itself, and without contributin to risk of injury-tosthe latter. r

he relative quantity of extra-heated air Y going to the furnace varies with the class of fuel, and may be so much as one half of the Whole for highly volatile fuels, suitable dampers such as it" being provided where necessafy to regulate the proportion of the two kinds of air. 7

The less-highly heated air from the upper or preliminary section'of the heater, viz the.

portion which is not passed through the lower or super-heating section, is'led by separate pipes or channels k to the space below ate, where oii'course it passes between the ars to startthe cqmbustion of the 'fuel in the usual way. Owing however to this at a lower temperature than it whole of the air-heater, it tends in fact to keep the temperature of the bars themselves lower even than it would be with an ordinary airheating system.

As regards the arrows in the drawing, 1 shows the direction of the cold in-coming air; 2, 2 show the paths of the less-heated air to the furnace and 3, 3 the divided path for that portion which goes into the hottest part of the heater, whence it passes (as the hotter air) by the path 47-4, into the top of the furnace, which it enters as at 5-5.

The arrows 6 show the paths of the flame and hot gases from the furnace to the heater g whilst 7 shows the path from the latter into the uptake.

In this way, an increased temperature is obtained in the combustion zone of the fursupply giving a correspondingly increased steaming power and efficiency of the boiler,

whilst the wear and tear on thegrate is less than it would be with an ordinary preheated air supply.

Moreover the ordinary combustion arch or radiator e such as common with automatic stokers, can be very much reduced in size or dispensed'with altogether, and thus the heat which it usually intercepts is allowed to reach the heating surface of the boiler by direct radiation, adding further to the efficiency and steaming power.

The combustion of the volatile distillates and of the carbon monoxide and other prod ucts ofprimary combustion, rising from the fuel, is thus promoted in the furnace itself,

namely well above the grate and therefore out of contact with the latter. The combustion which takes place on the grate itself is mainly that of the'fixed carbon in the fuel, and the temperature generated in the fuel bed is reduced on" this account, being still further lowered owing to the air from the ash-pit being cooler than it" the whole air supply were uniformly heated. Hence the risk of burning and damaging the grate is materially reduced.

The invention is furthern'lore particularly applicable to grates of the compartment type, or those in which the pressure of the air under the "rate is graduated to suit the diminishing thieliness of the fuel bed towards the back of the grate.

I claim In a steam boiler provided with a fine for waste gases and a furnace having a grate, the combination with said fine of a final air heater, an economizer and a preliminary air heater disposed therein and arranged to be traversed by the gases in the order named, means for conducting part of the air heated in the preliminary heater therefrom to a point below said grate, and means for conducting the rest of the heated air from said preliminary heater through said final heater to a point above said grate.

In testimony whereof I affix my signature.

' WILLIAM HENRY OWEN. 

